Methods and apparatus for adaptive filtering of signals of continuous analyte monitoring systems

Abstract

A method of filtering a signal in a continuous analyte monitoring system (CAM) includes applying adaptive filtering to the signal using an adaptive filter to generate a filtered continuous analyte monitoring signal during an analyte monitoring period, and increasing the adaptive filtering applied to the signal as a function of increasing noise on the signal. Other methods, apparatus, continuous analyte monitoring devices, and continuous glucose monitoring devices are also disclosed.

What is claimed is: 
     
       1. One or more non-transitory computer-readable media comprising computer-executable instructions that, when executed by at least one processor, perform a method of filtering a signal in a continuous analyte monitoring system, comprising:
 computing a noise level in an environment; 
 providing one or more biosensors comprising a working electrode and a counter electrode; 
 generating, using the one or more biosensors in the environment, the signal, wherein generating the signal comprises:
 applying a voltage across the working electrode and the counter electrode; 
 measuring a current associated with the working electrode, wherein the current is proportional to an analyte concentration in the environment; and 
 generating the signal using the current; 
 
 applying adaptive filtering to the signal using an adaptive filter to generate a filtered continuous analyte monitoring signal during an analyte monitoring period, wherein applying the adaptive filtering to the signal comprises:
 switching one or more low-pass filters into a closed state, the one or more low-pass filters including one or more cut-off frequencies, 
 wherein switching the one or more low-pass filters into the closed state is a function of the noise level such that all of the one or more low-pass filters are switched into the closed state when the noise level is zero; 
 passing the signal through the one or more low-pass filters such that one or more frequencies of the signal are filtered out upon reaching the one or more cut-off frequencies; and 
 changing the one or more cut-off frequencies as a function of the noise level; and 
 
 increasing the adaptive filtering applied as a function of increasing the noise level to a following signal generated by the one or more biosensors. 
 
     
     
       2. The one or more non-transitory computer-readable media of  claim 1 , wherein applying the adaptive filtering comprises increasing attenuation of the adaptive filter as a function of increasing the noise level. 
     
     
       3. The one or more non-transitory computer-readable media of  claim 1 , wherein computing the noise level in the environment comprises:
 measuring a plurality of signal points in the environment; and 
 computing a standard deviation based on the plurality of signal points. 
 
     
     
       4. The one or more non-transitory computer-readable media of  claim 1 , wherein the method further comprises:
 implanting the one or more biosensors at least partially in interstitial fluid; and 
 generating a measured current signal from the one or more biosensors, wherein applying the adaptive filtering comprises applying the adaptive filtering to the measured current signal. 
 
     
     
       5. The one or more non-transitory computer-readable media of  claim 1 , wherein generating, using the one or more biosensors in the environment, the signal further comprises:
 applying additional adaptive filtering to the current. 
 
     
     
       6. The one or more non-transitory computer-readable media of  claim 1 , wherein the method further comprises calculating the analyte concentration from a continuous analyte monitoring signal that is indicative of the analyte concentration, wherein applying the adaptive filtering to the signal comprises applying the adaptive filtering to the continuous analyte monitoring signal to generate the filtered continuous analyte monitoring signal. 
     
     
       7. The one or more non-transitory computer-readable media of  claim 6 , wherein the method further comprises analyzing the filtered continuous analyte monitoring signal to generate a trend in analyte concentrations during the analyte monitoring period. 
     
     
       8. The one or more non-transitory computer-readable media of  claim 1 , wherein the method further comprises causing display of at least a portion of the filtered continuous analyte monitoring signal on a display. 
     
     
       9. The one or more non-transitory computer-readable media of  claim 1 , wherein the method further comprises causing display of a trend in analyte concentrations on a display. 
     
     
       10. The one or more non-transitory computer-readable media of  claim 1 , wherein increasing the adaptive filtering comprises increasing attenuation in a stop band of at least one low-pass filter of the one or more low-pass filters as a function of noise on the signal during the analyte monitoring period. 
     
     
       11. The one or more non-transitory computer-readable media of  claim 1 , wherein applying the adaptive filtering to the signal comprises applying infinite impulse response filtering to the signal. 
     
     
       12. The one or more non-transitory computer-readable media of  claim 1 , wherein applying the adaptive filtering to the signal comprises applying finite impulse response filtering to the signal. 
     
     
       13. The one or more non-transitory computer-readable media of  claim 1 , wherein applying the adaptive filtering to the signal comprises applying filtering in a form of: S′(n)=alpha (R)*S(n)+(1−alpha (R))*S′(n−1), wherein the S′(n) is the filtered continuous analyte monitoring signal, S(n) is the signal, alpha(R) is a value less than or equal to 1.0, R is a noise estimate or measurement, and n is a sample number. 
     
     
       14. The one or more non-transitory computer-readable media of  claim 13 , wherein increasing the adaptive filtering applied to the signal as a function of a noise comprises decreasing the alpha(R) as a function of the noise. 
     
     
       15. The one or more non-transitory computer-readable media of  claim 13 , wherein the alpha(R) is calculated as baseAlpha−R*K, wherein the baseAlpha is a predetermined value and K is a constant that determines responsiveness of the alpha(R) to changes in noise. 
     
     
       16. The one or more non-transitory computer-readable media of  claim 15 , wherein the baseAlpha is in a range from 0.3 to 0.5. 
     
     
       17. The one or more non-transitory computer-readable media of  claim 15 , wherein the K is selected so that the alpha(R) is less than or equal to baseAlpha/2 when the R is at a maximum value. 
     
     
       18. The one or more non-transitory computer-readable media of  claim 1 , wherein applying the adaptive filtering to the signal comprises applying an exponential moving average to the signal. 
     
     
       19. The one or more non-transitory computer-readable media of  claim 1 , wherein an analyte in the continuous analyte monitoring system comprises glucose. 
     
     
       20. A method of continuous analyte monitoring (CAM), comprising:
 providing one or more biosensors comprising a working electrode and a counter electrode; 
 generating in an environment, using the one or more biosensors, a CAM signal, wherein
 generating in the environment the CAM signal comprises: 
 applying a voltage across the working electrode and the counter electrode; 
 measuring a current associated with the working electrode, wherein the current is proportional to an analyte concentration in the environment; and 
 generating the CAM signal using the current; 
 
 applying adaptive filtering to the CAM signal using an adaptive filter to generate an adaptively-filtered CAM signal, wherein applying the adaptive filtering comprises:
 computing a noise level in the environment; 
 switching one or more low-pass filters into a closed state, the one or more low-pass filters including one or more cut-off frequencies, 
 wherein switching the one or more low-pass filters into the closed state is a function of the noise level such that all of the one or more low-pass filters are switched into the closed state when the noise level is zero; 
 passing the CAM signal through the one or more low-pass filters such that one or more frequencies of the CAM signal are filtered out upon reaching the one or more cut-off frequencies; and 
 changing the one or more cut-off frequencies as a function of the noise level; and 
 
 increasing attenuation of the adaptive filtering as a function of increasing the noise level in the environment, wherein the adaptive filtering with increased attenuation is applied to a following CAM signal generated by the one or more biosensors. 
 
     
     
       21. The method of  claim 20 , wherein generating comprises calculating the CAM signal based on a signal generated by the one or more biosensors. 
     
     
       22. The method of  claim 20 , further comprising displaying at least a portion of the adaptively-filtered CAM signal on a display. 
     
     
       23. The method of  claim 20 , wherein applying the adaptive filtering to the CAM signal comprises applying infinite impulse response filtering to the CAM signal. 
     
     
       24. The method of  claim 20  wherein applying the adaptive filtering to the CAM signal comprises applying filtering in a form of: S′(n)=alpha(R)*S(n)+(1−alpha(R))*S′ (n−1), wherein S′ (n) is the adaptively-filtered CAM signal, S(n) is the CAM signal, the alpha(R) is a value less than or equal to 1.0, R is a noise estimate or measurement, and n is a sample number. 
     
     
       25. The method of  claim 24  wherein increasing the adaptive filtering applied to the CAM signal as a function of increasing the noise level in the environment comprises decreasing the alpha(R) as a function of the noise level. 
     
     
       26. The method of  claim 20 , wherein applying the adaptive filtering to the CAM signal comprises applying an exponential moving average to the CAM signal. 
     
     
       27. A continuous analyte monitoring system, comprising:
 one or more biosensors comprising a working electrode and a counter electrode, wherein the one or more biosensors are configured to general a signal; 
 an adaptive filter configured to increase filtering of the signal as a function of increasing noise on the signal, comprising:
 one or more low-pass filters having one or more cut-off frequencies; and 
 one or more filter switches electronically connected to the one or more low-pass filters, wherein the one or more filter switches are configured to toggle the one or more low-pass filters between a closed state and an open state; and 
 
 one or more non-transitory computer-readable media comprising computer-executable instructions that, when executed by at least one processor, perform a method of filtering the signal in the continuous analyte monitoring system, comprising:
 computing a noise level in an environment; 
 generating, using the one or more biosensors in the environment, the signal, wherein generating the signal comprises:
 applying a voltage across the working electrode and the counter electrode; 
 measuring a current associated with the working electrode, wherein the current is proportional to an analyte concentration in the environment; and
 generating the signal using the current; 
 
 
 applying adaptive filtering to the signal to generate a filtered continuous analyte monitoring signal during an analyte monitoring period, wherein applying the adaptive filtering to the signal comprises:
 switching the one or more low-pass filters into the closed state, 
 wherein switching the one or more low-pass filters into the closed state is a function of the noise level such that all of the one or more low-pass filters are switched into the closed state when the noise level is zero; 
 passing the signal through the one or more low-pass filters such that one or more frequencies of the signal are filtered out upon reaching the one or more cut-off frequencies; and 
 changing the one or more cut-off frequencies as a function of the noise level; and 
 
 increasing the adaptive filtering applied to the signal as a function of the noise level increasing to a following signal generated by the one or more biosensors.